Tire having tread for low temperature performance and wet traction

ABSTRACT

This invention relates to a tire with tread for promoting a combination of cold weather service at low temperatures and wet traction. The tread is of a rubber composition containing cis 1,4-polybutadiene and dual styrene/butadiene elastomers with reinforcing filler comprised of pre-hydrophobated precipitated silica and rubber reinforcing carbon black. The tread rubber composition may contain triglyceride vegetable oil such as soybean oil.

This invention relates to a tire with tread for promoting a combinationof cold weather service at low temperatures and wet traction. The treadis of a rubber composition containing cis 1,4-polybutadiene and dualstyrene/butadiene elastomers with reinforcing filler comprised ofprecipitated silica, which may be a pre-hydrophobated precipitatedsilica, and rubber reinforcing carbon black. The tread rubbercomposition contains triglyceride vegetable oil. The precipitated silicamay be derived from inorganic sand or from rice husks.

BACKGROUND OF THE INVENTION

Tires are sometimes desired with treads for promoting traction on wetsurfaces. Various rubber compositions may be proposed for tire treads.

For example, tire tread rubber compositions which contain high molecularweight, high Tg (high glass transition temperature) diene basedelastomer(s) might be desired for such purpose particularly for wettraction (traction of tire treads on wet road surfaces). Such tire treadmay be desired where its reinforcing filler is primarily precipitatedsilica which may therefore be considered as being precipitated silicarich.

When such elastomers have a high uncured rubber viscosity (e.g. Mooney,ML1+4. 100° C., viscosity), petroleum based rubber processing oil may beblended with the elastomer(s) to reduce the rubber composition's uncuredviscosity and to thereby promote more desirable processing conditionsfor the uncured rubber composition. The petroleum based rubberprocessing oil can be added to the elastomer prior to its addition to aninternal rubber mixer (e.g. a Banbury rubber mixer) or be added to therubber composition in the mixer to reduce the viscosity of the rubbercomposition both in the internal rubber mixer and for subsequent rubberprocessing such as in a rubber extruder.

Here, the challenge is to reduce the cured stiffness of such treadrubber compositions, as indicated by having a lower storage modulus G′at about −20° C., when the tread is intended to be also useful for lowtemperature winter conditions, particularly for vehicular snow driving.

It is considered that significant challenges are presented for providingsuch tire tread rubber compositions for maintaining their wet tractionwhile promoting low temperature (e.g. cold weather) performance.

To achieve such balance of tread rubber performances, it is proposed toevaluate providing a tread rubber composition containing a high Tg(glass transition temperature) elastomer together with an elastomerhaving a lower Tg to beneficially promote a lower stiffness of the curedrubber composition to improve cold weather performance of the tiretread, while substantially maintaining the tire tread's wet tractioncapability.

For such challenge, it is proposed to evaluate providing a combinationof high Tg and lower Tg styrene/butadiene elastomers together with a lowTg cis 1,4-polybutadiene rubber (PBd) with reinforcing filler comprisedof precipitated silica, which may be a pre-hydrophobated precipitatedsilica, and rubber reinforcing carbon black.

The combination of styrene/butadiene elastomers is proposed to becomprised of a relatively high Tg organic solvent polymerizationprepared styrene/butadiene elastomer (S-SBR) to promote wet traction,wherein the high Tg S-SBR is extended with triglyceride based vegetableoil to promote cold weather (winter) tire performance, together with alower Tg aqueous emulsion polymerization prepared styrene/butadieneelastomer (E-SBR), which is not oil extended, where the E-SBR has a Tgwhich lower than the Tg of the S-SBR, to beneficially promote loweringthe stiffness of the cured rubber composition at about −20° C. bycompensating for the presence of the higher Tg S-SBR to thereby furtherpromote cold weather (winter) performance for the rubber composition.

To meet the challenge of providing good cold weather (winter)performance while maintaining wet traction for the tire tread, it isalso desired to promote beneficial processability of the uncured rubbercomposition which contains the high Tg S-SBR by extending the S-SBR withvegetable oil instead of petroleum based rubber processing oil. Suchvegetable oil extension of the S-SBR further promotes a beneficiallylower cured stiffness of the tread rubber composition at lowertemperatures to thereby further promote cold weather performance for thetire tread.

Vegetable triglyceride oil extension of the high Tg S-SBR is to bedistinguished from free addition of the vegetable triglyceride oil tothe high Tg S-SBR or to the rubber composition. By the term “extension”it is meant that the vegetable oil is added to a cement comprised of acomposite of solvent solution of the high Tg S-SBR as a product ofpolymerization of styrene and 1,3-butadiene monomers is an organicsolvent solution with a suitable catalyst to promote the polymerization,wherein the high Tg S-SBR is recovered from the cement as a composite ofthe high Tg S-SBR and vegetable triglyceride oil.

The innovation of this approach thereby relies on the use of arelatively high Tg vegetable triglyceride oil extended high Tg S-SBRelastomer with a combination of with lower Tg E-SBR and low Tg PBdelastomers together with precipitated silica reinforcement which may bea pre-hydrophobated precipitated silica.

In one embodiment, the rubber composition may, if desired, also containfreely added vegetable triglyceride oil, in addition to vegetabletriglyceride oil contained in the vegetable oil extended high Tg SBR, tofurther promote a lower rubber stiffness at lower temperatures for thetread rubber. By the term “freely added”, it is meant that the vegetableoil is added to the rubber composition containing the S-SBR during itsphysical mixing of rubber and rubber compounding ingredients in contrastto the aforesaid “extending” of the high Tg S-SBR itself.

In one embodiment, to promote wet traction for such evaluation, withoutsignificantly detracting from the low temperature performance, it isdesired to further evaluate providing at least one traction resin in thetread rubber composition.

Historically it is recognized that triglyceride based vegetable oilssuch as, for example, soybean oil, has been previously suggested foraddition to various rubber compositions such as for example, and notintended to be limiting, in U.S. Pat. Nos. 7,919,553, 8,100,157,8,022,136 and 8,044,118.

However, while vegetable triglyceride oils have previously beenmentioned for use in various rubber compositions, including rubbercompositions for tire components, use of vegetable triglyceride oils asan extender oil for a high Tg S-SBR combined with a blend of lower TgPBd and E-SBR elastomers together with precipitated silicareinforcement, which may be in a form of pre-hydrophobated precipitatedsilica, is believed to be novel and a significant departure from pastpractice to both aid in processing of the uncured rubber composition andto provide cured rubber composition for a tire tread to promote acombination of wet traction and low temperature cold weatherperformance.

In the description of this invention, the terms “compounded” rubbercompositions and “compounds” are used to refer to rubber compositionswhich have been compounded, or blended, with appropriate rubbercompounding ingredients. The terms “rubber” and “elastomer” may be usedinterchangeably unless otherwise indicated. The amounts of materials areusually expressed in parts of material per 100 parts of rubber by weight(phr).

The glass transition temperature (Tg) of the solid elastomers may bedetermined by DSC (differential scanning calorimetry) measurements, aswould be understood and well known by one having skill in such art. Thesoftening point of a resin, where appropriate, may be determined by ASTME28 which might sometimes be referred to as a ring and ball softeningpoint.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a pneumatic tire is provided having acircumferential rubber tread intended to be ground-contacting, wheresaid tread is a rubber composition comprised of, based on parts byweight per 100 parts by weight elastomer (phr):

-   -   (A) 100 phr of a combination of conjugated diene-based        elastomers comprised of:        -   (1) about 10 to about 50, alternately from about 10 to about            30, phr of an organic solvent polymerization prepared high            Tg styrene/butadiene elastomer (high Tg S-SBR) having a Tg            in a range of from about −40° C. to about −30° C. with a            styrene content in a range of from about 30 to about 35            percent wherein said high Tg S-SBR is extended with from            about 10 to about 38 parts by weight per 100 parts of said            high Tg S-SBR of triglyceride vegetable oil (desirably to            the exclusion of petroleum based oil extension),        -   (2) about 10 to about 50, alternately from about 20 to about            40, phr of aqueous emulsion polymerization prepared            styrene/butadiene elastomer (E-SBR) having a Tg in a range            of from about −65° C. to about −45° C. with a styrene            content in a range of from about 15 to about 30 percent, and        -   (3) about 20 to about 60, alternately from about 30 to about            50, phr of cis 1,4-polybutadiene rubber having a cis            1,4-isomeric content of at least about 95 percent and having            a Tg in a range of from about −90° C. to about −108° C.,    -   (B) about 50 to about 250, alternately from about 75 to about        175, phr of rubber reinforcing filler comprised of precipitated        silica (amorphous synthetic precipitated silica) and rubber        reinforcing carbon black containing from about 2 to about 10 phr        of said rubber reinforcing carbon black, wherein said        precipitated silica is derived from silicon dioxide based        inorganic sand or from silicon dioxide containing rice husks and        is comprised of at least one of:        -   (1) pre-hydrophobated precipitated silica (hydrophobated            prior to its addition to the rubber composition) comprised            of precipitated silica pre-hydrophobated (pre-reacted) with            an alkoxyorganomercaptosilane or bis(3-triethoxysilylpropyl)            polysulfide containing an average of from about 2 about 4            connecting sulfur atoms in its polysulfidic bridge,            desirably an alkoxyorganomercaptosilane, to form a composite            thereof,        -   (2) precipitated silica having a nitrogen surface area in a            range of from about 140 to about 220 m²/g plus a silica            coupler having a moiety reactive with hydroxyl groups (e.g.            silanol groups) on said precipitated silica and another            different moiety interactive with said diene-based            elastomers, and        -   (3) precipitated silica having a nitrogen surface area in a            range of from about 90 to about 130 m²/g plus a silica            coupler having a moiety reactive with hydroxyl groups (e.g.            silanol groups) on said precipitated silica and another            different moiety interactive with said diene-based            elastomers,    -   (C) about 5 to about 45, alternately from about 7 to about 25,        phr of traction promoting resin comprised of at least one of        terpene, coumarone indene and styrene-alphamethylstyrene resins        where such resins desirably have a softening point (ASTM E28)        within a range of from about 60° C. to about 150° C., and

In one embodiment, said rubber composition contains about 5 to about 50,alternately from about 10 to about 30 phr of freely added vegetabletriglyceride oil (freely added to the rubber composition).

In further accordance with this invention, said tire having said tread,is provided as being sulfur cured.

Desirably, said precipitated silica is said pre-hydrophobated silica.Desirably said pre-hydrophobation of said precipitated silica is byreaction, and therefore a product of, the precipitated silica with analkoxyorganomercaptosilane.

When said precipitated silica is said pre-hydrophobated precipitatedsilica, additional precipitated silica (non-pre-hydrophobated silica)and/or said coupling agent may optionally be added to the rubbercomposition. Desirably, said coupling agent for the additionalprecipitated silica is comprised of bis(3-triethoxysilyl propyl)polysulfide having an average of from about 2 to about 4 connectingsulfur atoms in its polysulfide bridge.

In one embodiment, said vegetable triglyceride oil is comprised of acombination of saturated and unsaturated esters where said unsaturatedesters are comprised of a combination of at least one of oleic acidester, linoleate acid ester and linoleate acid ester. Said saturatedesters may be comprised of, for example and not intended to be limiting,at least one of stearic acid ester and palmitate acid ester.

In one embodiment, said vegetable triglyceride oil is comprised of atleast one of soybean oil, sunflower oil, rapeseed oil, canola oil,desirably soybean oil.

In one embodiment, the high Tg S-SBR desirably has a high molecularweight to thereby have an uncured Mooney viscosity (ML1+4), 100° C., ina range of from about 60 to about 120.

In one embodiment, the lower Tg E-SBR desirably is of a lower molecularweight than the S-SBR to thereby have an uncured Mooney viscosity(ML1+4), 100° C. in a range of from about 35 to about 50.

In one embodiment, the cis 1,4 polybutadiene rubber has a cis1,4-isomeric content of at least about 95 percent. It may, for example,have an uncured Mooney viscosity (ML1+4), 100° C., in a range of fromabout 45 to about 55.

In one embodiment, the tread rubber composition is desirably exclusiveof functionalized elastomers (e.g. functionalized styrene/butadieneelastomers).

In one embodiment, the tread rubber composition may contain afunctionalized elastomer (e.g. high Tg functionalized styrene/butadieneelastomer containing functional groups comprised of at least one ofamine, siloxy, thiol and carboxyl groups reactive with hydroxyl groupscontained on precipitated silica).

In one embodiment, said high Tg S-SBR (or said functionalized high Tgstyrene/butadiene elastomer) may be, if desired, a tin or siliconcoupled elastomer which would thereby increase its molecular weight anduncured Mooney viscosity.

In one embodiment, said traction promoting resin may be a terpene resincomprised of polymers of at least one of limonene, alpha pinene and betapinene and having a softening point within a range of from about 60° C.to about 140° C.

In one embodiment, said traction promoting resin may be a coumaroneindene resin having a softening point in a range of from about 60° C. toabout 150° C.

In one embodiment, said traction promoting resin may be astyrene-alphamethylstyrene resin having a softening point in a range offrom about 60° C. to about 125° C., alternately from about 80° C. to 90°C. (ASTM E28), and, for example, a styrene content of from about 10 toabout 30 percent.

In one embodiment, the precipitated silica is comprised of:

(A) a precipitated silica derived from inorganic sand (silicon dioxidebased sand), or

(B) a precipitated silica derived from rice husks (silicon dioxidecontaining rice husks).

In one embodiment the precipitates silica is derived from naturallyoccurring inorganic sand (e.g. SiO₂, silicon dioxide, which may containa trace mineral content). The inorganic sand is typically treated with astrong base such as, for example, sodium hydroxide, to form an aqueoussilicate solution (e.g. sodium silicate). A synthetic precipitatedsilica is formed therefrom by controlled treatment of the silicate withan acid (e.g. a mineral acid and/or acidifying gas such as, for example,carbon dioxide). Sometimes an electrolyte (e.g. sodium sulfate) may bepresent to promote formation of precipitated silica particles. Therecovered precipitated silica is an amorphous precipitated silica.

In one embodiment, the precipitated silica is a rice husk derivedprecipitated silica. Such precipitated silica is from derived rice planthusks (e.g. burnt ashes from rice husks) which contain SiO₂, silicondioxide, and which may contain trace minerals from the soil in which therice has been planted). In a similar methodology, the rice husks (e.g.rice husk ash) is typically treated with a strong base such as, forexample, sodium hydroxide, to form an aqueous silicate solution (e.g.sodium silicate) following which a synthetic precipitated silica isformed therefrom by controlled treatment of the silicate with an acid(e.g. a mineral acid and/or acidifying gas such as, for example, carbondioxide) in which an electrolyte (e.g. sodium sulfate) may be present topromote formation of precipitated silica particles derived from ricehusks. The recovered precipitated silica is an amorphous precipitatedsilica. For Example, see U.S. Patent Application Serial No.2003/0096900.

The precipitated silica, whether derived from the aforesaid silicondioxide or rice husks, may, for example, have a BET surface area, asmeasured using nitrogen gas, in the range of, for example, about 40 toabout 600, and more usually in a range of about 50 to about 300 squaremeters per gram. The BET method of measuring surface area might bedescribed, for example, in the Journal of the American Chemical Society,Volume 60, as well as ASTM D3037.

Such precipitated silicas may, for example, also have a dibutylphthalate (DBP) absorption value, for example, in a range of about 100to about 400, and more usually about 150 to about 300 cc/100 g.

Representative of such pre-hydrophobated precipitated silica may be, forexample, Agilon™ 400 from PPG.

Representative examples of rubber reinforcing carbon blacks are, forexample, and not intended to be limiting, referenced in The VanderbiltRubber Handbook, 13^(th) edition, 1990, on Pages 417 and 418 with theirASTM designations. Such rubber reinforcing carbon blacks may have iodineabsorptions ranging from, for example, 60 to 240 g/kg and DBP valuesranging from 34 to 150 cc/100 g.

Representative of silica coupler for said precipitated silica are:

(A) bis(3-trialkoxysilylalkyl) polysulfide containing an average inrange of from about 2 to about 4, alternatively from about 2 to about2.6 or from about 3.2 to about 3.8, sulfur atoms in its connectingbridge, or

(B) an alkoxyorganomercaptosilane, or

(C) their combination.

Representative of such bis(3-trialkoxysilylalkyl) polysulfide iscomprised of bis(3-triethoxysilylpropyl) polysulfide.

Said pre-hydrophobated precipitated silica is desirably a product ofprecipitated silica and an alkoxyorganomercaptosilane.

Said added precipitated silica (a non-hydrophobated precipitated silica)is desirably added to the rubber composition in combination with saidbis(3-triethoxysilylpropyl) polysulfide for reaction thereof in situwithin the rubber composition.

It is readily understood by those having skill in the art that thevulcanizable rubber composition would be compounded by methods generallyknown in the rubber compounding art. In addition said compositions couldalso contain fatty acid, zinc oxide, waxes, antioxidants, antiozonantsand peptizing agents. As known to those skilled in the art, depending onthe intended use of the sulfur vulcanizable and sulfur-vulcanizedmaterial (rubbers), the additives mentioned above are selected andcommonly used in conventional amounts. Representative examples of sulfurdonors include elemental sulfur (free sulfur), an amine disulfide,polymeric polysulfide and sulfur olefin adducts. Usually it is desiredthat the sulfur-vulcanizing agent is elemental sulfur. Thesulfur-vulcanizing agent may be used in an amount ranging, for example,from about 0.5 to 8 phr, with a range of from about 1 to 6 phr beingsometimes desired. Typical amounts of processing aids, if used, maycomprise, for example, about 1 to about 10 phr.

Typical amounts of antioxidants may comprise, for example, about 1 toabout 5 phr. Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others, such as, for example, thosedisclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through346. Typical amounts of antiozonants may comprise, for example, about 1to 5 phr. Typical amounts of fatty acids, if used, which can include,for example, stearic, palmitic and oleic acids, particularly a mixturecomprised thereof, in an amount, for example, ranging from about 0.5 toabout 6 phr. Typical amounts of zinc oxide may comprise, for example,about 0.5 to about 5 phr. Typical amounts of waxes, if used, maycomprise, for example, about 0.5 to about 5 phr. Such wax is often amicrocrystalline wax. Typical amounts of peptizers, when used, may beused in amounts of, for example, about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Sulfur vulcanization accelerators are used to control the time and/ortemperature required for vulcanization and to improve the properties ofthe vulcanizate. In one embodiment, a single accelerator system may beused, i.e., primary accelerator. The primary accelerator(s) may be usedin total amounts ranging, for example, from about 0.5 to about 4,sometimes desirably about 0.8 to about 3, phr. In another embodiment,combinations of a primary and a secondary accelerator might be used withthe secondary accelerator being used in amounts, such as, for example,from about 0.05 to about 3 phr, in order to activate and to improve theproperties of the vulcanizate. Combinations of these accelerators mightbe expected to produce a synergistic effect on the final properties andare somewhat better than those produced by use of either acceleratoralone. In addition, delayed action accelerators may be used which arenot affected by normal processing temperatures but produce asatisfactory cure at ordinary vulcanization temperatures. Vulcanizationretarders might also be used. Suitable types of accelerators that may beused in the present invention are amines, disulfides, guanidines,thioureas, thiazoles, sulfenamides, and xanthates. Often desirably theprimary accelerator is a sulfenamide. If a second accelerator is used,the secondary accelerator is often desirably a guanidine such as, forexample, a diphenylguanidine or zinc dibenzyl dithiocarbamate.

The mixing of the vulcanizable rubber composition can be accomplished bymethods known to those having skill in the rubber mixing art. Forexample, the ingredients are typically mixed in at least two stages,namely at least one non-productive stage followed by a productive mixstage. The final curatives, including sulfur-vulcanizing agents, aretypically mixed in the final stage which is conventionally called the“productive” mix stage in which the mixing typically occurs at atemperature, or ultimate temperature, lower than the mix temperature(s)of the preceding non-productive mix stage(s). The terms “non-productive”and “productive” mix stages are well known to those having skill in therubber mixing art. The rubber composition may be subjected to athermomechanical mixing step. The thermomechanical mixing step generallycomprises a mechanical working in a mixer or extruder for a period oftime suitable in order to produce a rubber temperature between 140° C.and 190° C. The appropriate duration of the thermomechanical workingvaries as a function of the operating conditions and the volume andnature of the components. For example, the thermomechanical working maybe from 1 to 20 minutes.

Vulcanization of the pneumatic tire containing the tire tread of thepresent invention is generally carried out at conventional temperaturesin a range of, for example, from about 140° C. to 200° C. Often it isdesired that the vulcanization is conducted at temperatures ranging fromabout 150° C. to about 170° C. Any of the usual vulcanization processesmay be used such as heating in a press or mold, heating with superheatedsteam or hot air. Such tires can be built, shaped, molded and cured byvarious methods which are known and will be readily apparent to thosehaving skill in such art.

The following examples are presented for the purposes of illustratingand not limiting the present invention. The parts and percentages areparts by weight, usually parts by weight per 100 parts by weight rubber(phr) unless otherwise indicated.

EXAMPLE I

In this example, exemplary rubber compositions for a tire tread wereprepared for evaluation for use to promote wet traction and cold weather(winter) performance. A Control rubber composition was prepared asControl rubber Sample A with a precipitated silica reinforced rubbercomposition containing styrene/butadiene rubber and cis1,4-polybutadiene rubber together with a silica coupler for theprecipitated silica reinforcement.

Experimental rubber compositions were prepared as Experimental rubberSamples B, C and D with various combinations of styrene/butadieneelastomers (high Tg S-SBR, including soybean oil extended high Tg S-SBR,and lower Tg E-SBR) together with low Tg cis 1,4-polybutsdiene rubber,pre-hydrophobated precipitated silica reinforcing filler and freelyadded soybean oil. A summary of the rubber compositions are illustratedin the following Table 1.

TABLE 1 Parts by Weight (phr) Control Experimental Material A B C DStyrene/butadiene rubber (S-SBR-A)¹ 67 0 0 0 Styrene/butadiene rubber(S-SBR-B)² 0 30 30 50 Styrene/butadiene rubber (E-SBR)³ 0 31 31 15 Cis1,4-polybutadiene rubber⁴ 33 44 44 44 Rubber processing oil⁵ 27 0 0 0Soybean oil, freely added⁶ 0 12 12 8 Traction resin⁷ 7.5 20 20 10Precipitated silica⁸ 95 0 0 0 Silica coupler⁹ 7.6 0 0 0Pre-hydrophobated precipitated silica¹⁰ 0 110 95 105 Fatty acids¹¹ 5 2 22 Carbon black (N120) 4 2 2 2 Wax (microcrystalline and paraffinic) 1.51.5 1.5 1.5 Antioxidants 2.8 2.8 2.8 2.8 Zinc oxide 1.8 1.8 1.8 1.8Sulfur 1.6 1.2 1.2 1.2 Sulfur cure accelerators¹² 4.5 3.3 3.3 3.3 ¹Anorganic solvent polymerization prepared styrene/butadiene rubber(S-SBR-A) having a Tg of about −23° C. and a styrene content of about 21percent as Sprintan ™ SLR4602 from Trinseo ²An organic solventpolymerization prepared styrene/butadiene rubber (S-SBR-B) having a Tgof about −35° C. and a styrene content of about 33 from The GoodyearTire & Rubber Company extended with about 20 parts by weight soybean oilper 100 parts by weight of the S-SBR-B ³An aqueous emulsionpolymerization prepared styrene/butadiene rubber (E-SBR) having a Tg ofabout −55° C. and a styrene content of about 23.5 percent as PLF1502from The Goodyear Tire & Rubber Company ⁴A cis 1,4-polybutadieneelastomer having a cis 1,4- content of about 96 percent and a Tg ofabout −106° C. as BUD1223 ™ from The Goodyear Tire & Rubber Company⁵Rubber processing oil primarily comprised of naphthenic oil ⁶Soybeanoil freely added to the rubber composition in a sense of not used toextend the styrene/butadiene rubber, as Sterling Oil from Stratus FoodCompany or Master Chef Soybean Oil 22393 from Cargill as a triglyceridesoybean oil ⁷Traction promoting resin as styrene-alphamethylstyrenecopolymer having a softening point in a range of about 80° C. to 90° C.(ASTM E28) and a styrene content in a range of from about 10 to about 30percent as Eastman Impera ™ P1504 from Eastman Chemical ⁸Precipitatedsilica as Zeosil 1165MP ™ from Solvay (derived from inorganic sand)⁹Silica coupler comprised of a bis(3-triethoxysilylpropyl) polysulfidecontaining an average in a range of from about 2 to about 2.6 connectingsulfur atoms in its polysulfidic bridge as Si266 from Evonik. Thecoupler was used without carbon black as a carrier. ¹⁰Pre-hydrphobatedprecipitated silica, precipitated silica treated with analkoxyorganomercaptosilane, as Agilon 400 ™ from PPG Industries ¹¹Fattyacids comprised of stearic, palmitic and oleic acids ¹²Sulfur cureaccelerators as sulfenamide primary accelerator and diphenylguanidine orzinc dibenzyl dithiocarbamate

The rubber Samples were prepared by similar mixing procedures, whereinthe elastomers and compounding ingredients were mixed together in afirst non-productive mixing stage (NP1) in an internal rubber mixer forabout 4 minutes to temperatures between about 140° C. and about 160° C.The resulting mixtures were subsequently mixed in a second sequentialnon-productive mixing stage (NP2) in an internal rubber mixer totemperatures between about 140° C. and about 160° C. Optionally therubber compositions were subsequently mixed in a third sequentialnon-productive mixing stage (NP3) in an internal rubber mixer to atemperature between about 140° C. and about 160° C. The rubbercompositions were subsequently mixed in a productive mixing stage (P) inan internal rubber mixer with a sulfur cure package, namely sulfur andsulfur cure accelerator(s), for about 2 minutes to a temperature ofabout 115° C. The rubber compositions were each removed from itsinternal mixer after each mixing step and cooled to below 40° C. betweeneach individual non-productive mixing stage and before the finalproductive mixing stage.

The following Table 2 illustrates cure behavior and various physicalproperties of rubber compositions based upon the basic formulation ofTable 1 and reported herein as Control rubber Sample A and Experimentalrubber Samples B, C and D. Where cured rubber samples are reported, suchas for the stress-strain, hot rebound and hardness values, the rubbersamples were cured for about 14 minutes at a temperature of about 160°C.

To establish the predictive wet traction, a tangent delta (tan delta)test was run at 0° C.

To establish the predictive low temperature (cold weather) performance,the cured rubber's stiffness (storage modulus G′) test was run at −20°C. and the rebound value at 100° C. was used for predictive rollingresistance performance.

TABLE 2 Parts by Weight (phr) Control Experimental A B C D MaterialStyrene/butadiene rubber 67 0 0 0 (S-SBR-A) Styrene/butadiene rubber 6730 30 50 (S-SBR-B) Styrene/butadiene rubber (E-SBR) 0 31 31 15 Cis1,4-polybutadiene rubber 0 44 44 44 Rubber processing oil 27 0 0 0Soybean oil, freely added 0 12 12 8 Pre-hydrophobated precipitated 0 11095 105 silica Tackifying resin 7.5 20 20 10 Properties Wet TractionLaboratory Prediction Tan delta (at 0° C., 0.42 0.35 0.35 0.35 3%strain, 10 Hertz) Cold Weather (Winter) Performance (Stiffness)Laboratory Prediction Storage modulus (G′), (MPa) 15.7 14.4 12.8 13 at−20° C., 10 Hertz, 3% strain (lower stiffness values are better) RollingResistance (RR) Laboratory Prediction (predictive hysteresis) Rebound at100° C., (%), 61 58 63 59 higher is better) Additional propertiesTensile strength (MPa) 17.5 15.3 16.2 15.8 Elongation at break (%) 392617 610 548 Modulus (Die C) 300% (MPa) 12.2 6.9 6.8 8.3

From Table 2 it is observed that snow traction at low temperatures in asense of stiffness is predictably improved, in a sense of lowerdetermined stiffness values at −20° C., of 14.4, 12.8 and 13,respectively, for Experimental rubber compositions B, C and D comparedto a stiffness value of 15.7 for Control rubber composition A, with onlyslight detriment to predictive wet traction in a sense of tan deltavalues of 0.35 for Experimental rubber compositions B, C and D ascompared to a tan delta value of 0.42 for Control rubber composition A.

From Table 2 it is observed that the hysteresis is beneficiallymaintained by Experimental rubber compositions B, C and D as compared toControl rubber composition A in a sense of hot rebound (100° C.) valuesof 58, 63 and 59 percent, respectively, for Experimental rubbercompositions B, C and D compared to a value of 61 percent for Controlrubber composition A.

It is thereby concluded that Experimental rubber compositions B, C andD, which were comprised of a combination of soybean oil extended organicsolution polymerization prepared styrene/butadiene rubber, aqueousemulsion polymerization prepared styrene/butadiene rubber and cis1,4-polybutadiene rubber together with reinforcing filler composed ofpre-hydrophobated precipitated silica, and traction promoting resincomposed of styrene-alphamethylstyrene resin provided a discovery of abeneficial combination of low temperature stiffness (G′) properties,predictive of low temperature cold weather traction, while maintaining alow temperature tan delta property, predictive of wet traction andsatisfactory hysteresis, predictive of satisfactory rolling resistance,for a tire with tread of such rubber composition.

EXAMPLE II

Experimental passenger automobile pneumatic tires of size 215/60R 16were prepared with treads comprised of rubber composition Control A andExperimental rubber compositions B, C and D of Example I andcorrespondingly identified as Control A treaded tire and Experimental B,C and D treaded tires, respectfully.

The tires were mounted on rigid wheels and tested under low temperatureconditions. Results of the tire tests are reported in the followingTable 3 with the results for tires with treads of Control rubbercomposition A normalized to values of 100 and results for Experimentaltires with treads of rubber compositions B, C and D related to thenormalized values.

The values for Control A tire are normalized to a value of 100 and thevalues for Experimental B, C and D tires are compared to the normalizedvalues of 100 for Control A tire.

TABLE 3 Control Experimental A B C D Tire cold weather (winter) snowtraction 100 106 107 108 (higher is better) Tire wet traction (higher isbetter) 100 100 99 97 Tire rolling resistance (higher is indication 10097 99 93 of beneficially lower rolling resistance)

From Table 3 it can be seen that the pneumatic tires with treads ofExperimental rubber compositions B, C and D exhibited cold weather(winter) traction values of 106, 107 and 108 which were significantlyimproved over normalized value of 100 for tires with treads of Controlrubber composition A.

From Table 3 it can be seen that pneumatic tires with treads ofExperimental rubber compositions B, C and D exhibited wet tractionvalues of 100, 99 and 97 which were the same or similar to normalizedvalue of 100 for tires with treads of Control rubber composition A.

From Table 3 it can be seen that pneumatic tires with treads ofExperimental rubber compositions B, C and D exhibited rolling resistancevalues of 97, 99 and 93 similar to normalized values of 100 for tireswith treads of Control rubber composition A.

It is thereby concluded that pneumatic tires with treads of Experimentalrubber compositions B, C and D, which were comprised of a combination ofsoybean oil extended organic solution polymerization prepared high Tgstyrene/butadiene rubber, aqueous emulsion polymerization prepared lowerTg styrene/butadiene rubber and low Tg cis 1,4-polybutadiene rubbertogether with reinforcing filler composed of pre-hydrophobatedprecipitated silica, confirmed a discovery of a beneficial combinationof low temperature snow traction while substantially maintaining wettraction and satisfactory rolling resistance for such tires.

EXAMPLE III

In this example, additional exemplary rubber compositions for a tiretread were prepared for evaluation for use to promote wet traction andcold weather (winter) performance.

A Control rubber composition was prepared as Control rubber Sample Ewhich was a duplicate of Experimental rubber Sample B of Example I whichcontained a pre-hydrophobated precipitated silica (precipitated silicapre-treated with an alkoxyorganomercaptosilane) as Agilon 400™ from PPGIndustries.

Experimental rubber Samples F and G were similar to Control rubberSample E except that, instead of the pre-treated precipitated silica, aprecipitated silica was added to the rubber composition as Zeosil 1165™MP from Solvay for Experimental rubber Sample F and MFIL™ 125 from MadhuSilica for Experimental rubber Sample G. A silica coupler was added tothe rubber composition to couple the precipitated silica to thediene-based elastomers.

A summary of the rubber compositions are illustrated in the followingTable 4.

TABLE 4 Parts by Weight (phr) Control Experimental Material E F GStyrene/butadiene rubber (S-SBR-B)² 30 30 30 Styrene/butadiene rubber(E-SBR)³ 31 31 31 Cis 1,4-polybutadiene rubber⁴ 44 44 44 Soybean oil(freely added)⁶ 12 12 12 Traction resin⁷ 20 20 20 Pre-hydrophobatedsilica¹⁰ 110 0 0 Precipitated silica A¹³ 0 95 0 Precipitated silica B¹⁴0 0 105 Silica coupler⁹ 0 7.6 8.4 Fatty acids¹¹ 2 2 2 Carbon black(N120) 2 2 2 Wax (microcrystalline and paraffinic) 1.5 1.5 1.5Antioxidants 2.8 2.8 2.8 Zinc oxide 1.8 1.8 1.8 Sulfur 1.2 1.2 1.2Sulfur cure accelerators¹² 3.3 5 5 ²An organic solvent polymerizationprepared styrene/butadiene rubber (S-SBR-B) having a Tg of about −35° C.and a styrene content of about 33 from The Goodyear Tire & RubberCompany extended with about 20 parts by weight soybean oil per 100 partsby weight of the S-SBR-B ³An aqueous emulsion polymerization preparedstyrene/butadiene rubber (E-SBR) having a Tg of about −55° C. and astyrene content of about 23.5 percent as PLF1502 from The Goodyear Tire& Rubber Company ⁴A cis 1,4-polybutadiene elastomer having a cis 1,4-content of about 96 percent and a Tg of about −106° C. as BUD1223 ™ fromThe Goodyear Tire & Rubber Company ⁶Soybean oil freely added to therubber composition in a sense of not used to extend thestyrene/butadiene rubber, as Sterling Oil from Stratus Food Company orMaster Chef Soybean Oil 22393 from Cargill as a triglyceride soybean oil⁷Traction promoting resin as styrene-alphamethylstyrene copolymer havinga softening point in a range of about 80° C. to 90° C. (ASTM E28) and astyrene content in a range of from about 10 to about 30 percent asEastman Impera ™ P1504 from Eastman Chemical ⁹Silica coupler comprisedof a bis(3-triethoxysilylpropyl) polysulfide containing an average in arange of from about 2 to about 2.6 connecting sulfur atoms in itspolysulfidic bridge as Si266 from Evonik. The coupler was used withoutcarbon black as a carrier. ¹⁰Pre-hydrphobated precipitated silica,precipitated silica treated with an alkoxyorganomercaptosilane, asAgilon 400 ™ from PPG Industries ¹¹Fatty acids comprised of stearic,palmitic and oleic acids ¹²Sulfur cure accelerators as sulfenamideprimary accelerator and diphenylguanidine or zinc dibenzyldithiocarbamate ¹³Precipitated silica as Zeosil 1165MP ™ from Solvayhaving a reported BET nitrogen surface of about 160 m²/g ¹⁴Precipitatedsilica as MFIL ™ from Madkhu Silica having a reported BET nitrogensurface area of about 125 m²/g

The rubber Samples were prepared by similar mixing procedures, whereinthe elastomers and compounding ingredients were mixed together in afirst non-productive mixing stage (NP1) in an internal rubber mixer forabout 4 minutes to temperatures between about 140° C. and about 160° C.The resulting mixtures were subsequently mixed in a second sequentialnon-productive mixing stage (NP2) in an internal rubber mixer totemperatures between about 140° C. and about 160° C. Optionally therubber compositions were subsequently mixed in a third sequentialnon-productive mixing stage (NP3) in an internal rubber mixer to atemperature between about 140° C. and about 160° C. The rubbercompositions were subsequently mixed in a productive mixing stage (P) inan internal rubber mixer with a sulfur cure package, namely sulfur andsulfur cure accelerator(s), for about 2 minutes to a temperature ofabout 115° C. The rubber compositions were each removed from itsinternal mixer after each mixing step and cooled to below 40° C. betweeneach individual non-productive mixing stage and before the finalproductive mixing stage.

The following Table 5 illustrates cure behavior and various physicalproperties of rubber compositions based upon the basic formulation ofTable 4 and reported herein as Control rubber Sample E and Experimentalrubber Samples F and G. Where cured rubber samples are reported, such asfor the stress strain, hot rebound and hardness values, the rubbersamples were cured for about 14 minutes at a temperature of about 160°C.

To establish the predictive wet traction, a tangent delta (tan delta)test was run at 0° C.

To establish the predictive low temperature (cold weather) performance,the cured rubber's stiffness (storage modulus G′) test was run at −20°C. and the rebound value at 100° C. was used for predictive rollingresistance performance.

TABLE 5 Parts by Weight (phr) Control Experimental E F G MaterialStyrene/butadiene rubber (S-SBR-B) 30 30 30 Styrene/butadiene rubber(E-SBR) 31 31 31 Cis 1,4-polybutadiene rubber 44 44 44 Soybean oil,freely added 12 12 12 Traction resin 20 20 20 Pre-hydrophobated silica110 0 0 Precipitated silica A 0 95 0 Precipitated silica B 0 0 105Properties Wet Traction Laboratory Prediction Tan delta (at 0° C., 3%strain, 10 Hertz) 0.36 0.40 0.46 Cold Weather (Winter) Performance(Stiffness) Laboratory Prediction Storage modulus (G′), (MPa) at −20°C., 13.5 19.7 15.9 10 Hertz, 3% strain (lower stiffness values arebetter) Rolling Resistance (RR) Laboratory Prediction (predictivehysteresis) Rebound at 100° C. (%) (higher is better) 57.3 50.6 52.3Additional properties Tensile strength (MPa) 15.4 16.9 17.1 Elongationat break (%) 642 615 610 Modulus (Die C) 300% (MPa) 6.9 7.2 7.9

From Table 5 it is observed that cold weather performance indicators atlow temperatures in a sense of stiffness are better, in a sense of lowerdetermined stiffness value at −20° C., of 13.5 MPa for the Controlrubber composition E as compared to Stiffness values of 19.7 and 15.9for Experimental rubber compositions F and G, respectively, with only aslight detriment to predictive wet traction in a sense of tan deltavalue of 0.36 for Control rubber composition E as compared to tan deltavalues of 0.4 and 0.46 for Experimental rubber compositions F and G.

From Table 5 it is observed that the hysteresis (evidenced by reboundvalues) is beneficially maintained by Control rubber composition E ascompared to Experimental rubber composition F in a sense of hot rebound(100° C.) value of 57.3 percent for Control rubber composition Ecompared to values of 50.6 and 52.3 percent for Experimental rubbercompositions F and G, respectively.

It is thereby concluded that Control rubber composition E whichcontained 110 phr of the pre-hydrophobated precipitated silica togetherwith a combination of soybean oil extended organic solutionpolymerization prepared high Tg styrene/butadiene rubber, aqueousemulsion polymerization prepared lower Tg styrene/butadiene rubber andlow Tg cis 1,4-polybutadiene rubber provided a discovery of a beneficialcombination of low temperature stiffness (G′) properties, predictive oflow temperature cold weather traction, while maintaining a lowtemperature tan delta property, predictive of wet traction andsatisfactory hysteresis, predictive of satisfactory rolling resistance,for a tire with tread of such rubber composition.

While various embodiments and details have been shown for the purpose ofillustrating the invention, it will be apparent to those skilled in thisart that various changes and modifications may be made therein withoutdeparting from the spirit or scope of the invention.

What is claimed is:
 1. A pneumatic tire having a circumferential rubbertread of a rubber composition comprised of, based on parts by weight per100 parts by weight elastomer (phr): (A) 100 parts by weight of acombination of conjugated diene-based elastomers comprised of: (1) about10 to about 50 phr of an organic solvent polymerization prepared high Tgstyrene/butadiene elastomer having a Tg in a range of from about −40° C.to about −30° C. with a styrene content in a range of from about 30 toabout 35 weight percent wherein said high Tg S-SBR is extended with fromabout 10 to about 38 parts by weight per 100 parts of said high Tgstyrene/butadiene elastomer of triglyceride vegetable oil, (2) about 10to about 50 phr of aqueous emulsion polymerization preparedstyrene/butadiene elastomer having a Tg in a range of from about −65° C.to about −45° C. with a styrene content in a range of from about 15 toabout 30 weight percent, and (3) about 20 to about 60 phr of cis1,4-polybutadiene rubber having a cis 1,4-isomeric content of at leastabout 95 percent and having a Tg in a range of from about −100° C. toabout −108° C., (B) about 50 to about 250 phr of rubber reinforcingfiller comprised of a combination of precipitated silica derived fromsilicon dioxide based inorganic sand or from silicon dioxide containingrice husks and rubber reinforcing carbon black where said reinforcingfiller is comprised of from about 2 to about 10 phr of said rubberreinforcing carbon black, wherein said precipitated silica of saidreinforcing filler is comprised of at least one of: (1)pre-hydrophobated precipitated silica comprised of precipitated silicapre-hydrophobated with an alkoxyorganomercaptosilane orbis(3-triethoxysilylpropyl) polysulfide containing an average of fromabout 2 about 4 connecting sulfur atoms in its polysulfidic bridge toform a composite thereof, (2) precipitated silica having a nitrogensurface area in a range of from about 140 to about 220 m²/g togetherwith a silica coupler having a moiety reactive with hydroxyl groups onsaid precipitated silica and another different moiety interactive withsaid diene-based elastomers, and (3) precipitated silica having anitrogen surface area in a range of from about 90 to about 130 m²/gtogether with a silica coupler having a moiety reactive with hydroxylgroups on said precipitated silica and another different moietyinteractive with said diene-based elastomers, (C) about 5 to about 45phr of traction promoting resin comprised of at least one of terpene,coumarone indene and styrene-alphamethylstyrene resins having asoftening point within a range of from about 60° C. to about 150° C. 2.The tire of claim 1 wherein said rubber composition contains about 5 toabout 50 phr of freely added vegetable triglyceride oil.
 3. The tire ofclaim 2 wherein said freely added triglyceride vegetable oil iscomprised of at least one of soybean oil, sunflower oil, rapeseed oiland canola oil.
 4. The tire of claim 2 wherein said freely addedvegetable triglyceride oil is comprised of soybean oil.
 5. The tire ofclaim 1 wherein said precipitated silica is a pre-hydrophobatedprecipitated silica comprised of precipitated silica pre-hydrophobatedwith an alkoxyorganomercaptosilane or bis(3-triethoxysilylpropyl)polysulfide containing an average of from about 2 about 4 connectingsulfur atoms in its polysulfidic bridge to form a composite thereof. 6.The tire of claim 5 wherein said rubber composition contains anadditional precipitated silica.
 7. The tire of claim 5 wherein saidrubber composition contains an additional silica coupling agentcomprised of a bis(3-triethoxysilyl propyl) polysulfide having anaverage of from about 2 to about 4 connecting sulfur atoms in itspolysulfide bridge.
 8. The tire of claim 1 wherein said precipitatedsilica is a pre-hydrophobated precipitated silica comprised ofprecipitated silica pre-hydrophobated with an alkoxyorganomercaptosilaneto form a composite thereof.
 9. The tire of claim 8 wherein said rubbercomposition contains an additional precipitated silica.
 10. The tire ofclaim 8 wherein said rubber composition contains an additionalprecipitated silica together with a silica coupling agent comprised of abis(3-triethoxysilyl propyl) polysulfide having an average of from about2 to about 4 connecting sulfur atoms in its polysulfide bridge.
 11. Thetire of claim 1 wherein said precipitated silica is a precipitatedsilica having a nitrogen surface area in a range of from about 140 toabout 220 m²/g together with a silica coupler having a moiety reactivewith hydroxyl groups on said precipitated silica and another differentmoiety interactive with said diene-based elastomers comprised of atleast one of alkoxyorganomercaptane and bis (3-triethoxysilylpropyl)containing an average of from about 2 to about 4 connecting sulfur atomsin its polysulfidic bridge.
 12. The tire of claim 1 wherein saidprecipitated silica is a precipitated silica having a nitrogen surfacearea in a range of from about 90 to about 130 m²/g together with asilica coupler having a moiety reactive with hydroxyl groups on saidprecipitated silica and another different moiety interactive with saiddiene-based elastomers comprised of at least one ofalkoxyorganomercaptane and bis (3-triethoxysilylpropyl) containing anaverage of from about 2 to about 4 connecting sulfur atoms in itspolysulfidic bridge.
 13. The tire of claim 1 wherein said triglyceridevegetable oil for said styrene/butadiene elastomer oil extension iscomprised of at least one of soybean oil, sunflower oil, rapeseed oiland canola oil.
 14. The tire of claim 1 wherein said triglyceridevegetable oil for said styrene/butadiene elastomer oil extension iscomprised of soybean oil.
 15. The tire of claim 1 wherein said high Tgstyrene/butadiene elastomer has an uncured Mooney viscosity (ML1+4),100° C., in a range of from about 60 to about
 120. 16. The tire of claim1 wherein said high Tg styrene/butadiene elastomer is tin or siliconcoupled.
 17. The tire of claim 1 wherein said high Tg styrene/butadieneelastomer is a functionalized elastomer containing at least one ofamine, siloxy, thiol and carboxyl groups reactive with hydroxyl groupson said precipitated silica.
 18. The tire of claim 1 wherein saidtraction promoting resin is a styrene/alphamethylstyrene resin having asoftening point in a range of from about 60° C. to about 125° C.
 19. Thetire of claim 1 wherein said precipitated silica is derived from silicondioxide based inorganic sand.
 20. The tire of claim 1 wherein saidprecipitated silica is derived from silicon dioxide containing ricehusks.